1. Field of the Invention
The present invention relates to a vacuum pump system for delivering light gases and including at least one high-vacuum pump.
2. Description of the Prior Art
A pump system for evacuating a receiver includes, e.g. a turbomolecular pump provided on the high-vacuum side and one or more fore-vacuum pumps for further delivering and for compressing to an atmospheric pressure gas that was condensed by the turbomolecular pump. These fore-vacuum pumps can be formed, e.g., as a combination of a rotary piston pump and a vane-type rotary pump, or as a dry compression pump discharged against atmospheric pressure. (DE-OS 38 28 608). Such pump systems are suitable for delivering and for compressing of gases with medium or high molecular weight (e.g., N2, O2, Ar). For pumping light gases (e.g., H2, He), these systems are less suitable, in particular, when it is necessary to deliver a large quantity of gases. In this case, often several high-vacuum pumps are provided on the high-vacuum side for suction of the produced gases.
Conventional fore-vacuum pump systems are not in position to handle a large quantity of gases that accumulates at the gas outlet of a high vacuum pump. Up to the present, the conventional fore-vacuum pumps proved to be hardly suitable for handling light gases. The rotary piston pumps have only a small compression rate, the vane-type rotary pumps are not oil-free. They should be provided with a cooling system in which oil condences. This requires increased operational expenses and complicates the structure of the pumping system.
To improve transportation of light gases, often, a carrier gas is used. However, this solution is likewise associated with increased expenses. In addition, in this case, measures need to be taken to subsequently separate the gases. Moreover, the carrier gas adversely affects the fore-vacuum pressure and, thus, the pump characteristics of the entire system.
In many cases, the fore-vacuum system is spaced by a large distance from high-vacuum pump outlet, which results in increased conductance losses.
An object of the present invention is to provided a pump system suitable for pumping a large quantity of gases of which the light gases are the main component. The conventional system should be converted in a pump system suitable for achieving the object of the invention, using simple means.